Contemporary research on neural networks and neural systems demands versatile techniques for sampling electrical and biochemical parameters of neural activity. An especially pressing technical problem is that of measuring multiple chemical or electrical changes simultaneously within a functioning neural system. The problem of simultaneously stimulating multiple components of a neural system chemically or electrically has been equally daunting. The present proposal concerns the development of a chronically implantable brain probe that allows both biochemical and electrical events to be monitored at up to 12 loci (per probe) simultaneously in freely-behaving subjects. Our probe also provides the capability of simultaneous chemical or electrical stimulation as well as chemical and electrical monitoring. The overall aim of this proposal is to build and test prototypes of our multichannel chemical/electrical probes (MULTIPROBES). Specific experiments are planned for evaluating the characteristics of different recording electrode configurations and for determining the optimal design and dimensions of the fluid channels and ports of the chemical stimulating/recording channels. In addition, as a preliminary test of actual performance in vivo, prototype MULTIPROBES will be used to record hippocampal electrical field potentials while drugs are simultaneously administered to the tissue from the fluid ports of the probe.